Grinding mills and gap adjustment means therefor



Ma 1959 epw. EDWARDS ET AL 2,8

QRINDING MILLS AND GAP ADJUSTMENT MEANS THEREFOR Filed April 19, 1956 mm a a 2,876,958 p GRINDING MILLS AND GAP ADJUSTMENT MEANS THEREFOR George Wilfred Edwards and Roger Joseph Sevin,

- Paris, France Application April 19, 1956, Serial No. 579,223 Claims priority, application France April 20, 1955 -2 Claims. -(Cl. 241256) This invention relates to grinding mills.

1n grinding mills incorporating-the rotaryv grinding wheel or disc it is customary to determine the gap be tween such rotary grinding wheel or disc and a stationary grinding wheel or disc by adjusting them relatively to each other by means of a micro-meter screw or other mechanical device.

Once the relative positions are determined, it follows that if there are any variations in flow, or in the consistency of the substance being treated, the pressure between the grinding wheels or discs will vary, and this will affect the final result of the grinding operation. Moreover, it is not possible to control this pressure.

It is the chief object of the present invention to. overcome these disadvantages and to provide means whereby a selected pressure can be established, regulated, controlled and maintained constant during a grinding operation.

According to the present invention in a grinding mill incorporating cooperating grinding wheels or discs at least one of which is rotatable and one of. which is adjustable relatively to the other to vary the gap therebetween means are provided for applying an hydraulic or pneumatic pressure to the adjustable wheel or disc thereby to maintain a constant predetermined grinding pressure between said wheels or discs.

. In order that the said invention. may be clearlyunderstood and readily carried into effect the same will now be more fully described with reference to the accompanying drawing which shows one constructional embodiment in section.

In the embodiment illustrated the pressure is applied to the rotatable grinding wheel of a mill but if the stationary grinding wheel were so arranged as to be capable of being shifted longitudinally, the same principle could readily be adapted to the latter wheel.

Referring now to the drawing 1 denotes a main shaft which is supported by two bearings disposed within a bearing support sleeve 2 which is slidable longitudinally within a casing 3.

The grinding wheels are designated 7 and 11 and in order to adjust the gap between such wheels, the bearing support sleeve 2 is adapted to be moved translationally with respect to the casing 3 by means of a hand wheel 4 carrying two difierential screwthreads, one of which screws cooperates with a thread in the casing and the other with a thread on the bearing support sleeve. By allowing an appropriate lateral play to one of the screwthreads it will be realised that for a given position it is possible to have a corresponding amount of play in the translational movement of the bearing support sleeve with respect to the casing.

Screwed onto and centered on the shaft 1 is a grinding wheel support hub 5 which carries a plate 6 into which is fitted the movable grinding wheel 7. The wheel 7 is mounted on a sleeve 8 and is secured thereon by means of a nut 9 provided with vanes or blades 9a.

2,876,958 l atented Mar. 10,

The unit comprising the grinding wheel 7, the sleeve 8 and the vane or blade carrying the plate 6 and such unit is fixed in position by means of a nut 10.

The stationary grinding wheel 11 is supported in a cover 12 which is centered on and fixed to the front of the casing 3.

The product to be milled or homogenised is fed into a hopper 13 fixed to the cover 12 and on operation of the mill the product will be entrained by the vanes or blades on the nut 9 being sucked from the hopper 13 and forced into'the gap between the grinding wheels 7 and 11, the width of the said gap being adjustable by means of the hand wheel 4. As it passes between the grinding wheels, the product exerts pressure against the surface of the 'grindingwheels, tending to force the said wheels apart from one another. The reactioncaused by this pressure'will be taken up on the one hand by the bolts which secure the cover, and on the other hand by the'hand wheel 4. When discharged from the grinding wheels, the product is collected in the casing and delivered through a spout 14.

The shaft 1 is driven by means of a pulley 15 which is fixed on the said shaft at that end opposite the rotatable grinding wheel 7.

It will 'be seen from the foregoing that, for a given position of the hand wheel 4, the bearing support sleeve unit can be displaced forwards o1 rearwards within the limits corresponding to the lateral play given to the screwthreads of the hand wheel. in other words, for a mean gap width between grinding wheels given by the position of the hand wheel 4, the distance between grinding wheels is capable of variation within the limits of the lateral 'play between threads.

If there is applied to the shaft a pressure P equal to and acting in opposition to the pressure caused by the passage of the substance between the grinding wheels, it will be 'seen that the rotatable grinding wheel 7 will oscillate due to the efiect of these two thrusts, but that the oscillation will be limited and will correspond to the play allowed in the screwthreads of the hand wheel 4. --According to the invention the counter-pressure P 'is applied'to the shaft by hydraulic or pneumatic means in such a manner that the said pressure can easily be adjusted and controlled.

In the embodiment illustrated this principle is carried in'toelfect-inthe following manner:

Mounted on the end of that shaft 1 opposite to the grinding wheel 7 is a bearing 16 which centres a cup 17. Bearing on the one hand against the shaft 1 and on the other hand against the said cup is a thrust bearing 18. Thus a pressure P exerted on the cup will be transmitted to the shaft 1 and thence to the grinding wheel 7.

The pressure P is applied to the cup by means of a piston 19 slidable in the cylinder 20 which is fixed in relation to the casing 3. Connected to the chamber 21 of the said cylinder is a pressure gauge 22 which will thus indicate the value of the pressure P. The chamber 21 is fed with oil or water by means of a pump 23 which draws such liquid from a reservoir 24. A valve 25 provided with a spring, the tension of which can be adjusted by a handle 26, is arranged in a by-pass line between the discharge side of the pump 23 and the reservoir 24 and thus the pressure can be adjusted by operating said handle 26.

In order to reduce the pressure without touching the adjusting means, a second valve 27 is also provided such latter valve being disposed in a branch pipe between the discharge side of the pump 23 and the reservoir 24.

The following arrangement is provided in order to brake the movements of the bearing support sleeve 2 relative to the casing 3 and to prevent said sleeve from rotating -ii1 the essingehn the hand wheel 4 is operated.

A stepped screw 28 is screwed into the casing 3 and bears with a stepped portion against a brake shoe 30 which in this bears against the bearing support sleeve 2. The screw 28 also penetrates into a longitudinal slot 29 formed for this spur-po se said sleeve 2. Since the screw 28 is holldw, it an be used to obtain access to the bearihgs of the support sleeve in order to lubricate the said bearings.

The apparatus above described is adapted to operate in the following manner:

Let it be assumed that the pitch of the screwthreads er the hand wheel 4 are such that by turning thesame in a izldc'zlrwise direction the grinding wheels will be inoved fiir'th'e'r apart from eneanomer.

First 61? all "the grinding wheels are moved apart, the pump 23 is started up, "and the handle 26 is used t'o adju'st the desired "pressure, which will be indicated by the "pressure gauge 22. The movable grinding wheel 7 is then advanced by turning the hand wheel 4 in the counter-clockwise direction until the grindingwheels only just contact one another i. e. until the gap between the wheels is nill. This can be verified by turning the pulley 1-5 by hand.

At this instant the reaction of the pressure is entirely taken up by the screwthreads of the: hand wheel 4. It is then possible to till the hopper 13 and to start up the apparatus.

The product is drawn in from the hopper 13 and forced between the grinding wheels, where it exerts pressure against the grinding wheel 7. The pressure P can then be equilibrated by operating the handle 26. When the pressure P balances the pressure in thegap, the reaction on the screwthreads of the hand wheel 4 will disappear. Therefore, the point of equilibrium can be ascertained by the hand wheel 4 which, being relieved of any reaction, can be operated freely.

The apparatus with the arrangements described hereinbefore can be used with advantage in grinding substances in powdered form which are dispsersed in an excipient or in binding agents in a liquidorspasty condition,- such as paints, enamels, inks, chocolates etc., but it can be used generally to solve any problems of emulsification or bringing into intimate contact two or more liquids or prebrems of intimately mixing two or more substances in the pulverulent state.

1. In a grinding mill including a casing and cooperate ing grinding wheels mounted in the casing one of which is rotatable and mounted on a driving shaft which in turn is mounted in hearings in the casing, a rotatable screw threaded means carried by the casing and arranged for moving the rotatable driving shaft and the grinding wheel thereon toward and away from the other grinding wheel for adjusting the rotatable grinding wheel with respect to the other grinding wheel to vary the gap be tween said wheels; said rotatable screw threaded means having apredetermined amount of axial play in its thread structure, a thrust hearing at the end of the shaft opposite that of the rotatable grinding wheel, and a piston element for applying the pressure of a pressure fluid to the thrust hearing and to said end of the shaft for taking up the axial play in the thread structure of the screw threaded means and the axial thrust of the rotatable grinding wheel when the mill is effecting a grinding operation.

2. In a grinding mill including a 'casin'g and cooperating grinding wheels mounted in the casing one of which is rotatable and mounted on a driving shaft which in turn is mounted in hearings in the casing, a sleeve surrounding the driving shaft and in which the bearings for the shaft are mounted, said sleeve being movable axially with respect to the casing, a screw threaded means 'arranged between the casing and the sleeve formoving the rotatable grinding wheel, the shaft and the sleeve with respect to the casing and for adjusting the rotatable grinding wheel with respect to the other grinding wheel to vary the gap therebetween, said screw threaded means having a predetermined amount of axial play, a thrust bearing-at theend of the shaft opposite that of the-rotatable grinding wheel, and a piston element for applying the pressure of a pressure fluid to the thrust bearing and to said end of the shaft for taking up the axial play in the screw threaded means.

References Cited in the file of this patent UNITED STATES PATENTS German Oct. 29, 1953 

